Dragan Stevanovic, Faculty of Science and Mathematics, Visegradska 33, 18000 Nis, Serbia and Montenegro, e-mail: firstname.lastname@example.org
Abstract: We find all connected graphs in which any two distinct vertices have exactly two common neighbors, thus solving a problem by B. Zelinka.
Keywords: graphs, adjacency matrix, eigenvalues of a graph, common neighbours
Classification (MSC2000): 05C75, 05C50
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